The neuronal pathways through the limbic system through which olfactory and vomeronasal chemosensory inputs control reproductive physiology and behavior have been mapped in our laboratory in previous studies. Key areas along these pathways are the medial nucleus of the amygdala (M), the bed nucleus of the stria terminalis (BNST), and the medial preoptic area (MPOA). In addition to transmitting chemosensory information, neurons in these three regions actively concentrate circulating gonadal (steroid) hormones. We propose here to investigate the precise location, i.e., the cellular subgroups, within M, MPOA and BNST where transmission of vomeronasal and olfactory information might be influenced by the presence of gonadal hormones. We will use the male Syrian hamster as a model because in this animal both chemosensory inputs and testosterone are essential for mating behavior. We hypothesize specifically that testosterone is concentrated in neurons which are part of the vomeronasal pathway and that its absence alters the morphology of these neurons in ways that disrupt the flow of information along the pathway. We propose 1) to define interconnections between these areas in detail using HRP, fluorescent compounds and 3H amino acids as tracers, 2) to localize the subpopulations of cells within M, MPOA and BNST which concentrate testosterone using 3H-steroid autoradiography, 3) to identify those testosterone concentrating neurons in M which project to BNST and those projecting to MPOA, 4) to characterize the Golgi anatomy of neurons in M, MPOA and BNST, and 5) using the Golgi technique to quantify morphological changes in the dendrites of these neurons which result from long term castration. Our long range goal is to understand the cellular mechanisms which underline central nervous system integration of environmental and hormonal influences controlling reproductive physiology and behavior.